The present invention is generally directed to toner compositions, and more specifically to colored encapsulated toner compositions. In one embodiment, the present invention is related to colored magnetic toner compositions that can, for example, be selected for single component development, and more specifically for a number of inductive single component development processes. In an embodiment the present invention relates to toner compositions comprised of a polymer binder, a colorless or lightly colored magnetic material, especially a grayish (substantially gray in color) magnetite, a whitening agent, a color pigment, dye or mixture thereof, and a conductive fine powder comprised of metal oxide, such as, for example, powdered tin oxide or titanium oxide, or a mixture of metal oxides. In one specific embodiment of the present invention, there are provided colored magnetic encapsulated toner compositions comprised of a core comprised of a polymer binder, a substantially colorless magnetic material, a whitening agent, and a color pigment, and wherein the core is encapsulated in a polymeric coating such as a polyurea, a polyurethane, a polyamide, a polyester, or mixtures thereof, and wherein the shell contains a conductive powdered additive comprised of a conductive metal oxide of, for example, tin oxide doped with bismuth. The aforementioned encapsulated toner compositions generally possess a volume resistivity of from about 10.sup.3 to about 10.sup.8 ohm-cm, and preferably a volume resistivity of about 10.sup.4 to about 10.sup.6 ohm-cm. This level of toner conductivity is particularly suited for use in a number of inductive single component development systems. In another embodiment of the present invention, there is provided a colored magnetic encapsulated toner composition comprised of a core of an acrylic, methacrylic, styrene polymer binder, or the copolymeric derivatives thereof, such as poly(butyl methacrylate), lauryl methacrylate-stearyl methacrylate copolymer, styrene-butyl methacrylate copolymer, and the like, a colorless or slightly colored magnetic material, a whitener, and colored, other than black pigment particles, and encapsulated thereover a polymeric shell, wherein the shell has present thereon a conductive powder comprised of certain metal oxides, or mixtures thereof. The shell polymer of the present invention may contain a flexible structural moiety such as a polyether or polymethylene segment to improve its packing, and thus enhance resistance to core component diffusion or leaching through the toner shell structure. A further embodiment of the present invention relates to the preparation of conductive fine powdered metal oxides or mixed oxides, and their applications as toner conductivity control and surface release agents.
The metal oxide powders preferably possess a primary particle size, or average particle size diameter of less than about 1,000 Angstroms, and more preferably in average particle diameter of from about 100 to about 1,000 Angstroms. These powders can be optionally treated, preferably surface treated with certain organosilane reagents primarily to improve their powder flow properties. Specifically, the conductive powders can possess a specific resistivity of less than about 1,000 ohm-cm, and preferably less than about 100 ohm-cm such that when utilized as toner surface additives in an effective amount of, for example, generally less than 20 weight percent, they can impart to the toner a volume resistivity of from about 10.sup.3 to 10.sup.8 ohm-cm, and preferably from about 10.sup.4 to 10.sup.6 ohm-cm. Examples of advantages associated with the encapsulated compositions of the present invention in embodiments thereof include brilliant image color, and wide color variety; relatively high surface conductivity and thus suitability for use in many inductive single component development systems; cold pressure fixability; high image fix; nonagglomerating and excellent shelf-life stability of, for example, up to 2 years in some instances; and suitability for use in highlight color reprographic processes, especially xerographic and ionographic imaging and printing processes. Additionally, the use of the aforementioned conductive powders can also enhance the toner powder flow characteristics, thus eliminating, if desired, the utilization of other additives such as Aerosils, and zinc stearate for surface release and flow properties. Another advantage of the conductive oxide powder is related to its ability to reduce the toner's sensitivity to humidity.
The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. In one embodiment, the encapsulated toner compositions can be selected for pressure fixing processes wherein the image is fixed with pressure. Pressure fixing is common in ionographic processes in which latent images are generated on a dielectric receiver such as silicon carbide, reference U.S. Pat. No. 4,885,220, the disclosure of which is totally incorporated herein by reference and entitled Amorphous Silicon Carbide Electroreceptors. The latent images can then be toned with a conductive encapsulated toner of the present invention by inductive single component development, and transferred and fixed simultaneously (transfix) in one single step onto paper with pressure. Specifically, the toner compositions of the present invention can be selected for the commercial Delphax printers, such as the Delphax S9000.TM., S6000.TM., S4500.TM., S3000.TM., and Xerox Corporation printers such as the 4060.TM. and 4075.TM. wherein, for example, transfixing is utilized. In another embodiment, the toner compositions of the present invention can be utilized in xerographic imaging apparatuses wherein image toning and transfer are accomplished electrostatically, and transferred images are fixed in a separate step by means of a pressure roll with or without the assistance of thermal or photochemical energy fusing.
Encapsulated and cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy since, for example, these toner compositions can be fused at room temperature. Cold pressure fixability also enables the instant-on copy machine feature. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, the prior art colored toners, particularly magnetic colored toners, usually do not possess sufficiently low volume resistivity of, for example, 10.sup.4 to 10.sup.6 ohm-cm to be effectively useful for inductive single component development; the prior art magnetic colored toners also do not usually offer the desirable color quality or a wide color variety; and they are usually fixed under high pressure of, for example, in excess of 3,500 psi, which has a tendency to severely affect the image quality of the toner selected. Specifically, the high fixing pressure can lead to images of low resolution and severe image offset. Also, with some of the prior art cold pressure toner compositions inclusive of black toners, substantial image smearing can result from the high pressures selected. The high fixing pressure also generates in some instances objectionable paper calendering problems. In addition, a number of the prior art encapsulated toners, inclusive of black toners, often suffer from the known image ghosting problem when used in the transfix ionographic printers such as the Delphax printers. Additionally, the preparative processes of the prior art pressure fixable encapsulated toner compositions usually employ flammable organic solvents as the diluting vehicles and reaction media, and this could drastically increase the toner's manufacturing cost because of expensive solvent separation and recovery procedure, and the need for explosion-proof equipment, and the necessary precautions that have to be undertaken to prevent the solvent associated hazards. Moreover, the involvement of a solvent in the prior art processes also may decrease the product yield per unit volume of reactor size. Furthermore, with many of the prior art processes narrow size dispersity toner particles cannot be easily obtained by conventional bulk homogenization techniques as contrasted with the process of the present invention wherein narrow size dispersity toner particles can be more easily and economically obtained in embodiments thereof. These, and other disadvantages are eliminated, substantially eliminated, or minimized with the toners and process of the present invention. More specifically, with the encapsulated toners of the present invention, control of the toner surface conductivity, and toners with excellent color quality can be achieved. Also, with the encapsulated toners of the present invention undesirable leaching or loss of core components is minimized or avoided, and image ghosting is eliminated, in many instances, primarily because of the utilization of an impermeable polymeric shell in some embodiments. Image ghosting, which is one of the known common phenomena in transfix ionographic printing processes, refers to, for example, the contamination of dielectric receiver by residual toner materials which cannot be readily removed in the cleaning process. The result is the retention of latent images on the dielectric receiver surface after cleaning, and the subsequent unwarranted development of these images. One of the common causes of image ghosting is related to the leaching of the sticky core binder out to the toner's surface leading to their adherence to the dielectric receiver during the image development process.
In a patentability search report the following U.S. patents were listed: U.S. Pat. No. 4,803,144 which discloses an encapsulated toner with a core containing as a magnetizable substance, a magnetite, see Example 1, which is black in color, wherein on the outer surface of the shell there is provided a white electroconductive powder, preferably a metal oxide powder, such as zinc oxide, titanium oxide, tin oxide, silicon oxide, barium oxide and others, see column 3, line 59 to column 4; in column 8 it is indicated that the colorant can be carbon black, blue, yellow, and red; in column 14 it is indicated that the electroconductive toner was employed in a one component developing process with magnetic brush development, thus it is believed that the toner of this patent is substantially insulating; U.S. Pat. No. 4,937,167 which relates to controlling the electrical characteristics of encapsulated toners, see for example columns 7 and 8, wherein there is mentioned that the outer surface of the shell may contain optional surface additives 7, examples of which include fumed silicas, or fumed metal oxides onto the surfaces of which have been deposited charge additives, see column 17 for example; U.S. Pat. No. 4,734,350 which discloses an improved positively charged toner with modified charge additives comprised of flow aid compositions having chemically bonded thereto, or cemiadsorbed on the surface certain amino alcohol derivatives, see the Abstract for example; the disclosures of each of the aforementioned patents being totally incorporated herein by reference; and, which according to the search report are not significant but may be of some background interest U.S. Pat. Nos. 2,986,521; 4,051,077; 4,108,653; 4,301,228; 4,301,228 and 4,626,487.
In a patentability search report in a copending application U.S. Ser. No. 524,946, the disclosure of which is totally incorporated herein by reference, the following U.S. Pat. patents were listed: U.S. Pat. No. 4,514,484 directed to a powder suitable for developing latent images comprising of magnetic particles coated with a mixture of a thermoplastic resin and a silane, see for example the Abstract of the Disclosure; note column 3, beginning at line 15, wherein it is indicated that into the organic thermoplastic resin is incorporated a silane selected from those illustrated; also incorporated into the thermoplastic resin are magnetic materials, see column 3, beginning at line 35; U.S. Pat. No. 4,565,773 directed to dry toners surface coated with nonionic siloxane polyoxy alkalene copolymers with a polar end, see the Abstract of the Disclosure; and primarily of background interest is U.S. Pat. Nos. 4,640,881; 4,740,443; 4,803,144 and 4,097,404, the disclosure of which is totally incorporated herein by reference.
The following prior art, all U.S. patents, are mentioned: U.S. Pat. No. 4,770,968 directed to polysiloxane butadiene terpolymer toner resins, reference for example column 4, and note the formulas of FIGS. 1 to 6, including FIG. 2B, which toners can be selected wherein silicone release oils are avoided, with no apparent teaching in this patent directed to encapsulated toners; U.S. Pat. No. 4,814,253 directed to encapsulated toners comprised of domains containing a polymer component having dispersed therein a release composition and thereover a host resin component comprised of toner rein particles and pigment particles, see for example the Abstract of the Disclosure and column 4, and note column 4 wherein there is illustrated as one of the components of the encapsulated toner domains comprised of styrene butadiene block polymers such as Kraton, styrene copolymers, or styrene siloxanes, which components have entrapped or dissolved therein mineral oils or silicon oils; U.S. Pat. No. 4,430,408 relating to developer compositions containing a fluorene modified alkyl siloxane and a surface treatment carbon black, reference the Abstract of the Disclosure for example; U.S. Pat. No. 4,758,491 relating to dry toner and developer compositions with a multiphase polyorgano siloxane block or graft condensation copolymer, which provides polyorgano siloxane domains of a particular size and concentration at the toner particle surfaces; and U.S. Pat. No. 4,820,604 directed to toner compositions comprised of resin particles, pigment particles, and a sulfur containing organo polysiloxane wax such as those of the formulas illustrated in the Abstract of the Disclosure.
There are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there are disclosed in the prior art encapsulated toner compositions containing in some instances costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Moreover, illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process.
Disclosed in U.S. Pat. No. 5,045,422 entitled Encapsulated Toner Compositions, the disclosure of which is totally incorporated herein by reference, are encapsulated compositions containing cores comprised of a fluorocarbon-incorporated polymer binder. More specifically, there is illustrated in the aforementioned patent an encapsulated toner composition comprised of a core with a fluorocarbon-incorporated resin binder, pigment or dyes, and a polymeric shell; and an encapsulated toner composition comprised of a core comprised of a fluorocarbon-incorporated resin binder derived from the copolymerization of an addition-type monomer and a functionalized fluorocarbon compound represented by Formula (I), wherein A is a structural moiety containing an addition-polymerization functional group; B is a fluorine atom or a structural moiety containing an addition-polymerization functional group; and x is the number of difluoromethylene functions, pigment or dyes, and a polymeric shell. Also, illustrated in U.S. Pat. No. 5,013,630 entitled Encapsulated Toner Compositions, the disclosure of which is totally incorporated herein by reference, is an encapsulated toner composition comprised of a core comprised of pigments or dyes, and a polysiloxane-incorporated core binder, which core is encapsulated in a shell. Moreover, illustrated in U.S. Pat. No. 5,023,159, the disclosure of which is totally incorporated herein by reference, are encapsulated toners with a soft core comprised of silane modified polymer resin, a colorant, and a polymeric shell thereover. Specifically, in one embodiment there are disclosed in the aforementioned patent encapsulated toners comprised of a core containing a silane-modified polymer resin, preferably obtained by free-radical polymerization, silane-modified pigment particles or dyes and thereover a shell, preferably obtained by interfacial polymerization. U.S. Pat. No. 5,023,159 in one embodiment is directed to an encapsulated toner composition comprised of a core comprised of the polymer product of a monomer or monomers, and a polyfunctional organosilicon component, and more specifically wherein the core is comprised of a silane-modified polymer resin having incorporated therein an oxysilyl (I), a dioxysilyl (II), or a trioxysilyl (III) function of the following formulas, pigment, dye particles or mixtures thereof; and a polymeric shell. ##STR1##
The aforementioned toners can be prepared by a number of different processes including the chemical microencapsulation method which comprises (1) mixing or blending of a core monomer or monomers, a functionalized organosilane, a free radical initiator or initiators, pigment, and a shell monomer or monomers; (2) dispersing the resulting mixture of pigmented organic materials by high shear blending into stabilized microdroplets in an aqueous medium with the assistance of suitable dispersants or suspension agents; (3) thereafter subjecting the aforementioned stabilized microdroplets to a shell forming interfacial polycondensation; and (4) subsequently forming the core binder by heat induced free radical polymerization within the newly formed microcapsules. The shell forming interfacial polycondensation is generally accomplished at ambient temperature, but elevated temperatures may also be employed depending on the nature and functionality of the shell monomer selected. For the core polymer resin forming free radical polymerization, it is generally effected at a temperature of from ambient temperature to about 100.degree. C., and preferably from ambient or room temperature, about 25.degree. C. temperature to about 85.degree. C. In addition, more than one initiator may be utilized to enhance the polymerization conversion, and to generate the desiired molecular weight and molecular weight distribution. The toners of the present invention can be prepared by similar processes wherein there are added to the encapculated particles the conductive metal oxide powders instead of the colloidal graphite, known carbon blacks, such as Black Pearls available from Cabot Corporation, or mixtures thereof as disclosed in some of the aforementioned copending applications. Other substantial differences include the utilization of colorless or light colored magnetic material and whitening agent in the toners of the present invention.
Illustrated in copending application U.S. Ser. No. 609,316, the disclosure of which is totally incorporated herein by reference, are toners free of encapsulation and comprised, for example, of a polymer resin or resins, an optional waxy, lubricating or low surface energy substance, a colorless or light colored magnetic material, a color pigment, dye or mixture thereof excluding black, and a whitening agent, and wherein the surface of the toner contains a conductive metal oxide.
Accordingly, there is a need for colored encapsulated toner compositions, and in particular colored magnetic encapsulated toner compositions, with many of the advantages illustrated herein. Also, there is a need for pressure fixable colored magnetic encapsulated toners which provide high quality images with acceptable fixing levels of, for example, over 80 percent at low fixing pressure, of for example, 2,000 psi. Moreover, there is a need for colored magnetic encapsulated toners, wherein image ghosting and the like can be avoided or minimized. Furthermore, there is a need for nonagglomerating colored magnetic encapsulated toners which possess a long shelf life exceeding, for example, 12 months. Also, there is a need for colored magnetic encapsulated toners with excellent surface conductivity characteristics and a volume resistivity of, for example, from about 10.sup.3 ohm-cm to about 10.sup.8 ohm-cm, and preferably from about 10.sup.4 ohm-cm to about 10.sup.6 ohm-cm, thus enabling their use in a number of known inductive single component development systems. Furthermore, there is a need for colored magnetic encapsulated toners with excellent powder flow and surface release properties enabling their selection for use in imaging systems without the use of surface release fluids such as silicone oils to prevent image offsetting to the fixing or fuser roll. Still another need resides in the provision of colored magnetic toners that are insensitive to changes in humidity. There is also a need for conductive surface additives which are capable of imparting desirable levels of surface conductivity to colored toners without adversely affecting their image color quality. Another associated need resides in the provision of preparative quality. Another associated need resides in the provision of preparative processes for obtaining conductive powdered metal oxides and mixed oxides, such as, for example, tin oxides, which have primary particle sizes of less than about 1,000 Angstroms, and specific resistivities of less than 1,000 ohm-cm, and which powders are useful as surface conductivity control and release agents for colored magnetic toner compositions which are suitable for inductive single component development. Additionally, there is a need for simple and economic processes for the preparation of colored magnetic encapsulated toners. Specifically, there is a need for a chemical microencapsulation process for colored magnetic encapsulated toners, and which process involves a shell forming interfacial polycondensation and a core binder forming free radical polymerization, and wherein flammable organic solvents are not employed in their preparation in some embodiments. Moreover, there is a need for enhanced flexibility in the design and selection of the shell and core materials for pressure fixable colored magnetic encapsulated toners and/or flexibility in controlling the toner physical properties such as the bulk density, particle size, and size dispersity.